Crack resistant member and tower

ABSTRACT

A crack-resistant member for preventing crack propagation, a method of preventing crack propagation, and method of assembly a tower are provided. The crack-resistant member includes at least one insert attached to at least one removed portion at a predetermined location along a girth weld and adjacent a heat affected zone of the tower. The at least one insert is positioned perpendicular to a weld direction and intersecting the girth weld. The at least one insert prevents crack propagation in the girth weld of the tower.

CROSS REFERENCE TO RELATED APPLICATION

This application relates to and claims the benefit of U.S. patentapplication Ser. No. 13/598,140, filed Aug. 29, 2012, entitled “ACrack-Resistant Member, a Method of Preventing Crack Propagation, and aMethod of Assembling a Tower,” the disclosures of which are incorporatedby reference in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to towers. More specifically, toa crack-resistant member, a method of preventing crack propagation in atower, and a method of assembling a tower.

BACKGROUND OF THE INVENTION

Wind towers are fabricated by joining sections of thin-wall piping bybutt welding the sections together, end to end. Generally, adjacentsections are welded around a perimeter of a joint defined between theadjoining sections to form a unitary structure. These circumferential(girth) welds and the heat affected zones (HAZs) around the girth weldcreate a continuous metallurgical and mechanical notch.

The girth welds of tower may be subjected to flexural stresses caused byloads within the tower or induced by the tower during turbine operation.Specifically, high winds acting on the tower may cause increasedflexural stresses, and/or the weight of the turbine at the top of thetower and/or the operation of the turbine may induce high cyclevibrational flexural stresses within the tower. Over time, a combinationof these factors may cause the girth welds to be subjected to hightensile stresses, which may increase the probability of cracksinitiating and propagating at the welds. Weld cracking may reduce thelife span of the turbine tower, which in-turn may increase costsassociated with maintaining the tower.

Additionally, the continuous metallurgical and mechanical notch of thegirth welds and HAZ provides a homogenous path around the fullcircumference of the tower through which a fatigue crack may propagate.A fatigue crack, once initiated, may progress unimpeded beyond acritical size.

Therefore, a patch, a method of preventing crack propagation in a tower,and a method of assembling a tower that do not suffer from the abovedrawbacks is desirable in the art.

SUMMARY OF THE INVENTION

According to an exemplary embodiment of the present disclosure, acrack-resistant member for preventing crack propagation in a tower isprovided. The crack-resistant member includes at least one insertattached to at least one removed portion at a predetermined locationalong a girth weld and adjacent a heat affected zone of the tower. Theat least one insert is positioned perpendicular to a weld direction andintersecting the girth weld. The at least one insert prevents crackpropagation in the girth weld of the tower.

According to another exemplary embodiment of the present disclosure, amethod of assembling a tower is provided. The method includes providinga plurality of metal rings. The plurality of metal rings arecircumferentially joined with a girth weld, the girth weld creates anadjacent heat affected zone in each of the joined metal rings. At leastone portion of the girth weld and the adjacent heat affected zones areremoved, the at least one portion is at a predetermined location alongthe girth weld. A plurality of inserts are provided. The plurality ofinserts are attached over the at least one removed portion along thegirth weld. The plurality of inserts are positioned perpendicular to aweld direction and intersecting the girth weld. The steps ofcircumferentially joining through attaching are repeated until thedesired section length is achieved. The attachment members are securedto a first side and a second side of the each of the sections. Thesections are joined using the attachment members to form the tower. Theplurality of inserts prevent crack propagation in the joined metal ringsof the sections of the tower.

According to another exemplary embodiment of the present disclosure, amethod of preventing crack propagation in an assembled tower isprovided. The method includes identifying a crack along a girth weld ofa tower. At least one portion of the girth weld and a heat affected zoneare removed. The at least one portion is at a predetermined locationalong the girth weld and adjacent identified crack. A plurality ofinserts are provided. The plurality of inserts are attached over the atleast one removed portion along the girth weld, the plurality of insertsbeing positioned perpendicular to a weld direction and intersecting thegirth weld. The plurality of inserts prevent crack propagation in thegirth weld of the tower.

Other features and advantages of the present invention will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of a wind turbine tower of the presentdisclosure.

FIG. 2 is a perspective view of a portion of metal rings removed from atower of the present disclosure.

FIG. 3 is a perspective view of a section of a tower of the presentdisclosure.

FIG. 4 is a schematic of a crack-resistant member of an embodiment ofthe present disclosure.

FIG. 5 is a schematic of a crack-resistant member of an embodiment ofthe present disclosure.

FIG. 6 is a schematic of a crack-resistant member of an embodiment ofthe present disclosure.

FIG. 7 is a schematic of a crack-resistant member of an embodiment ofthe present disclosure.

FIG. 8 is a schematic sectional view of the weld and heat affected zonetaken in direction 8-8 of FIG. 4 of the present disclosure.

FIG. 9 is a schematic sectional view of a patch taken in direction 9-9of FIG. 4 of the present disclosure.

FIG. 10 is a flow chart of a method of assembling of the presentdisclosure.

FIG. 11 is a flow chart of method of preventing crack propagation in anassembled tower of the present disclosure.

Wherever possible, the same reference numbers will be used throughoutthe drawings to represent the same parts.

DETAILED DESCRIPTION OF THE INVENTION

Provided is a crack-resistant member, a method of preventing crackpropagation in a tower, and a method of assembling a tower.

One advantage of an embodiment of the present disclosure includespreventing catastrophic events from missing a weld defect duringinspection. Another advantage of an embodiment includes arresting growthof fatigue cracks in tower girth welds. Yet another advantage of anembodiment of the present disclosure includes improving reliability ofstructural integrity of tower. Another advantage of an embodiment of thepresent disclosure includes diverting fatigue cracks along a girth weldinto the base metal.

Towers are used to mount various items, such as but not limited to, windturbines, cellular communications, and other items. Although theexamples and figures depict a wind turbine tower, the examples are notso limiting. Wind turbines are typically categorized according to thevertical or horizontal axis about which the blades rotate. One so-calledhorizontal-axis wind generator is schematically illustrated in FIG. 1.This particular configuration for a wind turbine 100 includes a tower104 supporting a drive train 106 with a rotor 108 that is covered by aprotective enclosure referred to as a “nacelle.” The blades 110 arearranged at one end of the rotor 108, outside the nacelle, for driving agearbox 112 connected to an electrical generator 114 at the other end ofthe drive train 106 arranged inside the nacelle along with a controlsystem 116. An anemometer 118 is also provided on the nacelle forproviding information to the control system 116. As illustrated in FIG.1, tower 104 includes plurality of sections 126 joined by attachmentmembers 120 to form tower 104. Any number of sections 126 may be joinedto obtain desired wind turbine tower 104 height.

FIGS. 2-3 illustrate section 126 of tower 104. FIGS. 4-7 illustrate acrack-resistant member 140 for preventing crack propagation in a tower104. As illustrated in FIGS. 4-7, crack-resistant member 140 includes atleast one insert 350 attached to at least one removed portion 200 (seeFIG. 2) at a predetermined location along girth weld 122 and adjacent aheat affected zone (HAZ) 330 (see FIG. 8) of tower 104. At least oneinsert 350 is positioned perpendicular to weld direction 370 andintersecting girth weld 122. At least one insert 350 prevents crackpropagation, which is generally indicated by the arrow labeled 360, ingirth weld 122 of tower 104 (see FIG. 1).

FIG. 2 is a perspective view of metal rings 124 joined together by girthweld 122 to form section 126 of tower 104. Any number of metal rings 124may be joined together by girth weld 122 to form section 126. Generally,girth weld 122 is formed using a sub arc welding process. In the presentdisclosure, a portion 200 of metal rings 124 is removed along girth weld122 using any suitable process, such as, but not limited to, machining,grinding, metal cutting, arc cutting processes, and combinationsthereof. Removed portion 200 includes girth weld 122 and heat affectedzone 330 surrounding girth weld 122 (see FIG. 8). Removed portion 200may be a rectangular portion 214 cut through metal rings 124. In analternative embodiment, removed portion 200 may be a slot 216 cut intometal rings 124. FIG. 2 also illustrates a crack 210 in girth weld 122.Cracks 210 may form in girth weld 122 for any number of reasons, suchas, but not limited to, stress on girth weld 122. If not addressed,cracks 210 may continue to propagate along girth weld 122 and lead tocatastrophic failure of the structure of tower 104. In one embodiment,after identifying crack 212, at least one portion 200 of section 126 isremoved. Portion 200 removed is along weld direction 370 (see FIG. 4) ofgirth weld 122.

FIG. 3 is a perspective view of section 126 of tower 104 includingplurality of patches 140 at various predetermined locations along girthweld 122. Each crack-resistant member 140 covers removed portion 200(see FIG. 2) of girth weld 122 and heat affected zone 300 (see FIG. 8).Location of crack-resistant member 140 depends on the purpose ofcrack-resistant member 140. In one embodiment, crack-resistant member140 is used to strengthen girth weld 122. When crack-resistant member140 is used to strengthen girth weld 122, location of crack-resistantmember 140 is determined as a function of the fracture mechanics andload on the tower 104 from the nacelle. To strengthen girth weld 122,for example, crack-resistant member 140 is placed at three or as many assix locations equidistance around girth weld 122, depending on thecritical flaw size as determined by fracture mechanics analysis of theparticular weld relative to its location along the tower and theparticular load placed on that girth weld 122. The primary equationsused for fracture mechanics are K₁=Y_(σ)√{square root over (πa)} whereY_(σ) is a function of crack length and the thickness of the material,K_(c)=√{square root over (EG_(e))} (for plane stress), and

$K_{e} = \sqrt{\frac{{EG}_{0}}{1 - v^{2}}}$

(for plane strain). Fracture occurs when K₁≧K_(c). The above disclosedformulas are used to calculate the critical crack length (critical flawsize), and takes into account loading from wind, gear train, propellersize, and other wind turbine properties, know to those in the art. Inanother embodiment, crack-resistant member 140 is used to arrest crack210 (see FIG. 2) propagation. When crack-resistant member 140 is used toarrest crack propagation, location of crack-resistant member 140 isdependent on crack 210 location and weld direction 370 of girth weld370. To arrest crack propagation along girth weld 122, for example,crack-resistant member 140 is placed at three or as many as sixlocations equidistance around girth weld 122, depending on the criticalflaw size as determined by fracture mechanics analysis of the particulargirth weld 122 relative to its location along the tower and theparticular load placed on girth weld 122. As depicted in FIG. 3,plurality of metal rings 124 are attached by girth weld 122 to formsection 126. Attached to first end 132 and second end 134 of section 126are attachment members 120, such as, but not limited to, flanges orother attaching means to join sections 126 together to form tower 104.

FIGS. 4-7 are schematics of different embodiments of crack-resistantmember 140 of the present disclosure. As depicted in FIGS. 4-7,crack-resistant member 140 includes insert 350 and weld 344 attachinginsert to underlying metal ring 124. Insert 350 is positionedperpendicular to weld direction 370 and intersecting girth weld 122. Asused herein, “perpendicular to weld direction” means thatcrack-resistant member 140 is applied over weld in a direction thatintersects with the weld direction 370. Insert 350 may include a metalplate 352 or at least one weld bead 454. Width of weld bead 454 rangesfrom about 6.35 millimeters (about 0.25 inches) to about 38.1millimeters (1.5 inches). Depending on size of removed portion 200,insert 350 has a first dimension 400 and a second dimension 402. Firstdimension 400 is about 25.4 millimeters (1 inch) to about 101.6millimeters (4 inches), or alternatively about 30 millimeters to about90 millimeters, or alternatively about 40 millimeters to about 80millimeters. Second dimension 402 is about 50.8 millimeters (2 inches)to about 101.6 millimeters (4 inches), or alternatively about 55millimeters to about 95 millimeters, or alternatively about 60millimeters to about 90 millimeters. In one embodiment, first dimension400 and second dimension 402 are the same. To attach insert 350 tounderlying metal rings 124 a lower energy weld process is used. Suitablelower energy weld processes, include, but are not limited to, gastungsten arc welding (GTAW) and shielded metal arc welding (includingflux welding), to form weld 344. Using lower energy welding processprevents the formation of a heat affected zone when attaching insert 350to metal rings 124. Insert 350 has a greater material tensile strengththan girth weld 122 material tensile strength. Typical tower girth welds122 usually include an about 70 ksi tensile strength filler metal.Suitable examples of material for insert 350, include, materials havinga tensile strength of 70,000 psi or greater, which include, but are notlimited to, alloy steel plates having the following American Society forTesting and Materials (ASTM) designations: any grade of A 514, A 240type 201-2, A 240 type 202, and A 240 type 304N. Filler metal used tomake weld 344 also has a higher tensile strength than girth weld 122 andis generally includes a metal having about 80 ksi to about 90 ksitensile strength.

As shown in FIG. 4, insert 350 is a metal plate 352. Metal plate 352covers and slightly overlaps removed portion 200 (see FIG. 2). Metalplate 352 is attached to underlying metal rings 124 using a low energyweld process. In one embodiment, metal plate 352 is attached to innerdiameter 780 of metal rings 124, outer diameter 782 of metal rings 124,or combinations thereof (see FIG. 8). Thickness of metal plate 352 isabout 6.35 millimeters (0.25 inches) millimeters to about 50.8millimeters (2 inches), depending on tower height and location of ring124 in tower 104.

As shown in FIGS. 5-7, insert 350 is plurality of weld beads 454deposited over removed portion 200 (see FIG. 2). Plurality of weld beads454 intersect girth weld 122 and are formed on a portion of metal rings124. In FIG. 5, plurality of weld beads 454 are generally placed in thesame direction as weld direction 370. In FIG. 6, plurality of weld beads454 are perpendicular to weld direction 370. FIG. 7 is a single weldbead 454 covers removed portion 200, in this embodiment, small slot 216(see FIG. 2).

FIG. 8 is a sectional view of girth weld 122 prior to removing portion200 (see FIG. 2). As shown in FIG. 8, girth weld 122 is surrounded byheat affected zones 330 in metal rings 124. Heat affected zones 330include about 6.35 millimeters (0.25 inches) metal ring 124 surroundinggirth weld 122. The dashed lines 802 represent the area that is removedto form removed portion 200 (see FIG. 2).

FIG. 9 is a sectional view of crack-resistant member 140 applied toremoved portion 200 (see FIG. 2). Crack-resistant member 140 includesinsert 350 and weld 344. Crack-resistant member 140 attaches to metalrings 124. Crack-resistant member 140 may be applied to girth weld 122of sections 126 of tower 104. The number of patches 140 needed isgenerally a function of the load on girth weld 122 and length of girthweld 122 and fracture mechanics calculated for girth weld 122.

FIG. 10 is a flow chart describing a method 900 of assembling tower 104.Method 900 includes providing a plurality of metal rings 124 (see FIGS.2 and 3), step 901. Method 900 includes circumferentially joiningplurality of metal rings 124 with girth weld 122 (see FIGS. 2 and 3),step 903. Girth weld 122 creates an adjacent heat affected zone (HAZ)330 in each of joined metal rings 124 (see FIG. 7). Method 900 includesremoving at least one portion 200 of girth weld 122 and adjacent heataffected zones 300 (see FIG. 2), step 905. At least one portion 200 isat a predetermined location along girth weld 122. Method 900 includesproviding plurality of inserts 350 (see FIGS. 3-7), step 907. Method 900includes attaching plurality of inserts 350 over at least one removedportion 200 along girth weld 122 (see FIGS. 3-7), step 909. Plurality ofinserts 350 are positioned perpendicular to weld direction 370 andintersecting girth weld 122 (see FIGS. 4-7). Method 900 includesrepeating the steps of circumferentially joining, step 903, throughattaching, step 909, until desired section 126 length is achieved.Method 900 includes securing attachment members 120 to first side 132and second side 134 of sections 126 (see FIG. 3), step 911. Method 900includes joining sections 126 using attachment members 120 to form tower104 (see FIG. 1), step 913. Plurality of inserts 350 prevent crackpropagation in joined metal rings 124 of the sections of tower 104.

FIG. 11 is a flow chart describing a method of preventing crackpropagation in an assembled tower 104 (see FIG. 1). Method 1000 includesidentifying crack 210 along girth weld 122 of tower 104 (see FIG. 2),step 1001. Method 1000; includes removing at least one portion 200 ofgirth weld 122 and heat affected zone (HAZ) 330 (see FIG. 2), step 1003.At least one portion 200 is at a predetermined location along girth weld122 and adjacent identified crack 210 (see FIG. 2). Method 1000 includesproviding plurality of inserts 350 (see FIG. 3), step 1005. Method 1000includes attaching plurality of inserts 350 over at least one removedportion 200 along girth weld 122 (see FIGS. 2 and 3), step 1007.Plurality of inserts 350 are positioned perpendicular to weld direction370 and intersecting girth weld 122 (see FIGS. 4-7). Plurality ofinserts 350 prevent crack propagation in girth weld 122 of tower 104(see FIG. 1).

While the invention has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

What is claimed is:
 1. A crack-resistant member for preventing crackpropagation in a tower comprising: at least one insert attached to atleast one removed portion at a predetermined location along a girth weldand adjacent a heat affected zone of the tower, the at least one insertbeing positioned perpendicular to a weld direction and intersecting thegirth weld, wherein the at least one insert prevents crack propagationin the girth weld of the tower.
 2. The crack-resistant member of claim1, wherein the at least one insert has a greater material tensilestrength than the girth weld material tensile strength.
 3. Thecrack-resistant member of claim 1, wherein the at least one insertincludes a metal plate.
 4. The crack-resistant member of claim 1,wherein the at least one insert includes a plurality of weld beads.
 5. Acrack-resistant member for preventing crack propagation in a towercomprising: at least one insert attached to at least one removed portionat a predetermined location along a girth weld and adjacent a heataffected zone of the tower, the at least one insert: being positionedperpendicular to a weld direction; and having a plurality ofsubstantially linear edges, wherein the plurality of substantiallylinear edges: intersect the girth weld normal to the weld direction; andextend beyond the adjacent heat affected zones, wherein the at least oneinsert prevents fatigue crack propagation in the girth weld.
 6. Thecrack-resistant member of claim 5, wherein the at least one insert has agreater material tensile strength than the girth weld material tensilestrength.
 7. The crack-resistant member of claim 5, wherein the at leastone insert comprises a metal plate.
 8. The crack-resistant member ofclaim 5, wherein the at least one insert comprises a plurality of weldbeads.
 9. The crack-resistant member of claim 5, wherein thecrack-resistant member comprises a plurality of inserts.
 10. Thecrack-resistant member of claim 9, wherein the plurality of inserts areequidistant around the girth weld.
 11. The crack-resistant member ofclaim 5, wherein the attachment of the at least one insert to the atleast one removed portion comprises a gas tungsten arc weld or ashielded metal arc weld.
 12. A tower comprising a plurality of metalrings and at least one crack-resistant member for preventing crackpropagation in the tower, wherein: the plurality of metal rings compriseat least one girth weld, and at least one heat affected zone adjacent tothe at least one girth weld, circumferentially joining the plurality ofmetal rings; and the at least one crack-resistant member comprises atleast one insert attached to at least one removed portion at apredetermined location along the at least one girth weld and adjacentthe at least one heat affected zone, the at least one insert: beingpositioned perpendicular to a weld direction; and having a plurality ofsubstantially linear edges, wherein the plurality of substantiallylinear edges: intersect the at least one girth weld normal to the welddirection; and extend beyond the at least one adjacent heat affectedzones, wherein the at least one insert prevents fatigue crackpropagation in the at least one girth weld.
 13. The tower of claim 12,wherein the at least one insert has a greater material tensile strengththan the at least one girth weld material tensile strength.
 14. Thetower of claim 12, wherein the at least one insert comprises a metalplate.
 15. The tower of claim 12, wherein the at least one insertcomprises a plurality of weld beads.
 16. The tower of claim 12, whereinthe at least one crack-resistant member comprises a plurality ofinserts.
 17. The tower of claim 16, wherein the plurality of inserts areequidistant around the at least one girth weld.
 18. The tower of claim12, wherein the attachment of the at least one insert to the at leastone removed portion comprises a gas tungsten arc weld or a shieldedmetal arc weld.
 19. The tower of claim 12, wherein the at least onegirth weld comprises a sub arc weld.
 20. The tower of claim 12, whereinthe tower is a wind tower.